Telephone-exchange system



Mar. 13, 1923.

P. C. SMITH TELEPHONE EXCHANGE SYSTEM Filed Sept. 50 1919 5 sheeta-sheet 1 Mar, 13, 1923.

P. c. SMITH TELEPHONE EXCHANGE SYSTEM Filed Sept 50, 1919-.

5 sheets-sheet 2 Mar. 12., 1923. 1,448,420

P c. SMITH I TELEPHONE EXCHANGE SYSTEM Filed Sept. 50, 1919 5sheets-sheet 5 Patented Mar. 13,

TPJC COMPANY,

' YORK.

ESTER, MASSACHUSETTS, ASSIGNOR T0 ESTERN ELEC5 A ooarom rron OF NEWTELEPHONE-EXCHANGE SYSTEM.

Application filed September 30, 1919. Serial No. 327,545.

T 0 all whom it may concern Be it known that I, PERCY C. SMITH, a

citizen of the United States, residing at This invention rel terns, and

Worcester and have invented cer- T eleof whiclithe folates to telephonesysmore particularly to systems in which the talking connection from thecallingto the called subscribers line is established by means ofautomatic or mechanically controlled switching devices.

.Heretofore it has been the common practice to extend a calli ngsubscribers line to an idle selector switch by means of a-switch of therotarytype,.eithei individual to the calling line or individual to thefirst selector trunk.

obviate the necessity of employing switches by providing a connectingthereby avoiding rotary of the relay type, switch parts, increasTheobject of this invention is to rotary switch ing the speed ofconnection, and simplifying the switch structure.

In its broadest aspect the invention resides in the provision ofa ing acapacity for serving ing lines and having access switch preferablyhavone hundred callto a group of ten trunks, which is adapted, to extenda calling line terminating therein,

to a pre-selected trunk line through the operation of a single relayindividual to the calling line.

The

line extension is therefore substantially instantaneous and need not bedelayed during the search for an idle trunk as has been necessary insystems employing rotary finder switches.

nets and so co-ordinated one for each calling line relays is necessary,

that a minimum of having access to the switch and one for each trunkoutgoing from example in aunit serving one the switch. Thus for hundred:lines and having access to ten trunks there are only one hundred and tenrelays.

The invention will now be describedin connection with one specificembodiment of the genus of my invention. In the accompanying drawings:

Figures 1 and 2 w hen placed end to end with Fig. 2 at the right ofFig.1 show a diagram of circuit connections illustrating the manner inwhich my inventionis incorporated in an automatic telephone system. Fig.1 shows the circuit of my improved line switch and selector andaconnector switch; v Figure 3 is a front elevational view of my improvedline switch unit, the trunk pre-selecting relays having been omitted forthe sake of clearness; v c i I Figure 4 is a vertical sectional Viewtaken on the line H of Fig. 3;

Figure 5 is a transverse sectional view taken on the line 5-5 of .Fig..4; i I Figure 6 is a detail plan :view of-one of the trunkpro-selecting relaysyand Figure 7 is a detail elevational view of theline extending relays.

Any step-by-step' two-movement switch may be employed with-theci-rcuitsshown. A switch. of this general character is shown in thepatent to Keith and Erickson No. 815,176, althoughpreferably a switchso. constructed as to operate the circuits disclosed in the patent toMartin No. 1,155,672 is employed. Although the features, of theinventionv are of one above referred to, they ,are equally applicable ina system employing ,switches of other types, as forexainple, powerdriven switches. 7

With each directively controlled switch is associated a circuit changingdevice for controlling the operating circuits of its respective switch.These devices vmay be of the generalcharacter of the switchwhich isshown in Keith and Erickson and. referred. to as a side switch.

Referring toliigs. 3 to 7 inclusive of the drawings, I have disclosedanimproved line Fig. 2 shows the circuit of a disclosed in-jasystememploy lllgStQP-bY-SllQP switches of the general type the abovementioned patent to 1 these vertical bars being provided upon their endswith out-turned extensions by means of which they are secured to the topand bottom plates by machine screws 7.

Supported between the vertical bars 8 and at is a series ofsuper-imposed relays or line 'magnets 8, preferably fifty, and supportedbetween the bars 5 and 6 is a second series of similar relays, therelays of the two series being positioned back to back as most clearlydisclosed in Fig. 4-.

Each relay 8 comprises an L-shaped tail piece 9 having a verticallydisposed arm 10 and a forwardly extending horizontally disposed arm 11bent downwardly at each end as at 12 and 13 for attachment to thevertical frame bars. In Fig. 3 the extensions 12 and 13 are shownattached to the "frame bars 3 and 1 by machine screws 14:. The extesions also serve to space the superinnoosed relays at suitable intervalsfrom each other, the extensions of the lowermost relay spacing thatrelay from the bottom plate 1 and the extensions of each sue essiverelay resting upon the horizontal arm 11 of the relay tail piece nextbeneath it to space such relays apart. Extending horizontally from thearm 10 of the tail piece is a core-piece 15. This core-piece liesparallel with the 11 of the tail piece and extends substantiallythewhole length of the tail piece. Wound upon the core-piece 15 is a doublewound winding comprising a high resistance operating winding 16 and alow resistance looking or holding winding 17.

The forward edge of the horizontal arm 11 of the tail piece is suitablynotched and between the projecting ears 18 thus formed, a plurality ofdepending armatures 19 are pivoted by means of a pivot pin 20 extendingthrough apertures in the ears and in the armatures. Each relay ispreferably equipped with ten armatures which are adapted to be attractedtoward the core piece 15, the magnetic circuit for each armaturecomprising a core 15, the vertical arm 10 of the tail piece 9, thehorizontal arm 11 thereof and the armature.

Normally each armature of each relay is held away from the forward endof the core 15 by means of a finger 21 secured to the front face of thearmature as by rivets 22, and engaging a hooked spring 23 secured to thetail piece 9, a distance suflicient to remove the armature from theinfluence of the core 15 so that in such position it is not possible forthe core 15 to attract the armature. The retractive movement of eacharmature is restrained by the engagement of the rearwardly extendingportion 2 1 of the spring 21 with the arm 11 of the tail piece. Eacharmature through the finger 21 is adapted to control a set of contactsprings as shown most clearly in Fig. 7. The ten sets of springs of eachrelay are suitably mounted between strips of insulating material and aresupported upon the tail-piece of the relay by screws 25. The springs ofthe several relays of the switch unit are multipled together in themanner shown in Fig. 1.

Pivotally supported in plates'29 and 30 secured to the top and bottomplates 2 and 1 respectively of the switch, immediately in front of thearmatures of each series of relays 8, is a group of ten verticallydisposed rods or actuating bars 26. Each rod is assigned to an outgoingtrunk line and is provided with a series. of fifty pins. 2-7 forcooperation with an armature of each of the series of fifty relays. Thusthe first trunk rod of each group is adapted to cooperate with the No. 1armature of each relay, the second trunk rod of each group with the No.2 armature of each relay etc. Normally these rods stand in a positionwith their pins resting upon the widened portions 28 of the fingers 21of the arma-tures, permitting the springs 23 to force the armatures awayfrom the pole pieces of the relays and out of the magnetic influencethereof. Upon the rotation of one of these rods the pins 27 Lin thereonforce an armature of each relay toward the pole pieces of the relays sothat upon a subsequent energization of one of the relays its armaturewhich has been positioned by the rotated trunk rod 26 will be attracted.

For the purpose of rotating the trunk rods 26, ten magnets 31 areprovided. F or convenience in mounting and to enable a more compactarrangement of the switch, these magnets are divided into two groupssecured respectively upon opposite sides of the switch and preferably ata point midway of its height, to bracket members 32 attached to theupright members 8, 4, 5 and 60f the switch frame by screws 33. Eachmagnet comprises a tail-piece 34- having a horizontally extendingportion 35, a core 36 and a winding T, the portion35 also extendingdownwardly below the lower edge of the tailpiece at to form means bywhich the magnet is secured to the bracket member 32, as shown mostclearly in Fig. 4. Any suitable means of attachment may be employed suchas screws 37.

Secured to each rod 26 is an arm 38, the arms of alternate rods of eachseries of rods extending from the rods in the same direction and servingas armatures for the magnets 81, the arms of the remaining intermediaterods of each series extending in the opposite direction, as most clearlydisclosed in Fig. 5. The arms 38 of corresponding rods of the twoseries, that is of rods individual to the same trunk and positioned onopposite sides of the switch frame, are interlinked by links 39 securedto the arms by screws 40 in such manner that when a trunk magnet 81attracts an arm 88 of a trunk rod 26. which it controls, the trunk rod26 corl. l. O

. snaps back of the piece 34 and side of the switch serve as armatures,the

ari'ns of corresponding rods upon the opposite side of theswitch andlinked thereto, serving merely as rocker-arms for transmitting thereciprocatorymovement of the connecting links 39 into a rotary movementofthe rods 26.

The armature arms 38-are normally held in retracted position, by springs41 secured thereto by pins 42 and'connccted to 'a central bar 43 bypins'44, the bar 43 being se-' cured at either end to the bracketmembers 32 vby screws 45. In its retracted position each of thesearmatures maintains a pair of contact springs 46 and 47 in contact bymeans of a stud 48of insulating material attached to the backofthearmature and resting against the end of spring 46, but permits thesprings to separate when attracted toward its core36; The springs are 1suitably insulatedvfrom each other and insulatedly mounted upon abracket strip 49 extending between the side bars of the switch frame. Asshown most clearly in. Fig. '6 the tail piece 34 of the magnet 31 isextended into close-associationwith the rod 26 which it controls toestablish a substantially closed magnetic circuit between the tail pieceand the armature 38 thereby increasing the chiciency of the magnet. r

After having been rotated by the magnet 31 through the energization ofthe winding T the trunkrod '26 is locked in its rotated position by ahook member 50, which is pivoted to the member 35 of the magnet asby ascrew 51 and which engages the .end of the armature 38. The hooked endof the member is urged toward the: end of'armature 38by a spring52 whichis-secured at its ends to the hook member andto the armature by pins 53as most clearly shown in Fig. 6. Normally of the armature 38 the beveledend 54 of the hook rests in contact with the, beveled end of thearmature 38 as shown in Fig. 5 but hook upon being attracted. The lockedup armature is released by means of a releasing magnet R- which ismounted upon the tail piece .34 withits core 55 secured in theextension. 35 of the. tail piece in alinement withthe core-piece 36 ofthe winding T. The two magnets R- andT3 thusare united in a single unitbut have separate magnetic circuits. The armature 56 of the I magnet Ris pivoted to the'end of the tail held in its retracted position in' the"retracted position by :means ofa spring 57 secured to the end of thearmature and to .thetail-piece by pins 58.

The with a laterally extending pin 59 which engages the cammed end=60.ofthe hook member 50. Up winding R the armaturethrough the pin- 59,-forces :the left hand end .of the hook member 50 toward the magnetwindingasviewed in Fig. 6,- thereby. moving the hooked end 54 awayfrom'theflend .of armature'38to release it.

Having thus acter of the apparatus which is. used in the systemembodying. the principles'ofmy invention, I'Will'DOW describe the.process by which a calling subscriberv A whose station is illustrated.at the left in Fig. 1, establishes connection with the subscriber AWhose station is illustrated. at the right in Fig. 2 and whose exchangenumber :we 'will assume to be 225.

When the subscriber A removeshis receiver preparatory tomaking a call, acircuit iscompleted in the usual manner through the windings of the linerelay '61,

which is energized and completes a circuit;

from grounded battery, through winding 16 of the relay 8, andthroughthefront'contact of relay 61 toground. The connecting relay 7tion that trunk No. VII leading toa group of first selectors to whichthe group of lines in which subscribers station A is located,

described the general char- 8 is energizedand-upon the assumpfree endof: armature 56 isprovided v on energization of themagnetf has beenpreselected for use in a manner hereinafter described and the trunk'rod26 has positioned the No.4 armaturejof each connecting relay 8 of thegroup of lines in a position to'be attracted by therelay 8, the armature'19 of the calling s'ubscribers connecting; relay will be attracted.'Since however the remaining armatures of theenergized relay8arenormally out 'of the field of magnetic influence of the; relay, they arenot attracted. The armatures of the re maining relays of the group whichhave been positioned by tracted at thistime since'their respectiverelays 8 are not energized.

Uponthe attraction of thearmature 19 of relay 8 the set of normally opencontacts with which it cooperates ;is closed. The' closure ,ofcontacts-62 and 63, and 64 w and 65 extends the talking conductors of the callingline by the' heavy conductors to the line relay 66 of the. idle firstselector'E which has been 'pre-selectedfor; use. This circuit. extendsFig. 2, through the left hand-winding of the line relay66, through thefirst position contact andwi-per- 67*of the sideswitch of the firstselector,overthelowerhcavy trunk conductor to the spring 62, through thespring 63,- through the-calhng subscribers line'loop,

the trunk rod 26 are not aty from grounded battery in through thesprings 64 and 65, over the upper heavy trunk conductor, through. theside-switch wiper 68 and its first position contact, through the righthand winding of the line relay 66, and back to the ground.

The line relay 66 energizes and closes a circuit for the slow actingrelease relay 69, shown at the right in Fig. l, which extends fromgrounded battery, through the winding of relay 69, through the frontcontact and armature of relay 66 to ground. Relay 69 upon energizingcloses a locking circuit for the relay 8, an energizing circuit for thecut-off relay of the calling line, closes an energizing circuit for atrunk relay T of the next idle trunk of the group of trunks-to which theline switch has access, and prepares the stepping circuit of theselected first selector. The locking circuit of the connecting relay 8may be traced from grounded battery through the locking winding 17 ofthe relay 8, through the closed contacts'70 and 71 of relay 8, throughthe closed contacts 72 and 73 of relay 69, to ground. The lockingwinding 17 while energizing the relay 8 sufiL ciently to maintain itsarmature 19 attracted, does not provide a sufficiently strongenergization to attract other armatures should other trunk rods beoperated to position other of its armatures within the field of force.

A branch of the locking circuit just traced extends through the windingof. the cut oif relay 74 of the calling line to grounded battery. Thisrelay upon energizing opens the circuit of the line relay 61 in theusual manner, which upon deener izing opens the initial energizingcircuit t rough the winding 16 of the connecting relay 8.

Upon the energization of the relay 8 a circuit was also closed throughthe releasing or unlocking magnet R which extends from groundedbatterythrough the winding R through contacts 7 5 and 76 to ground. The magnetR upon energization attract-s its armature 56, thereby oscillating thehook 50 to release the locked up armature 38 of the trunk magnet T whichupon releasing permits the restoration of the trunk rod 26 under theinfluence of the spring 41. The rod 26 in turn permits the restorationof all the armatures of relays 8.which it controls, out of the field ofmagnetic influence of the relays 8 with which they are associated, withthe exception of the armature 19 of the energized relay 8 which throu,,h the influence of holding windin 17 is malntained attracted.

When the relay 69 became energized it closed a circuit to preselectanother idle trunk for the next call, and assuming that the next trunkin the series No. VIII is at this time idle, a circuit is establishedfor its winding T which extends from grounded battery through the windinT through the normally closed contacts I7 and 7 8 of the release relayindividual to the selector to which the trunk N 0. VIII extends, throughthe alternate contacts 116 and 79 of the energized relay 69 through thecontacts 80 and 81 corresponding to contacts l6 and 47 disclosed in Fig.4 of magnet T of the trunk seized by the calling line, which contactsclosed when the armature 38 was re leased as above described, and back'to round. Upon the energization of winding T the trunk rod 26 of trunkVIII is rotated to position the armatures of the re lays 8 as previouslydescribed, and is locked in the rotated position by the hook memberassociated therewith independent of the 0011- tinued energization ofrelay 69. I

If upon the energization of the relay 69 the next trunk VIII had beenbusy, the following circuit for the magnet winding T of trunk No. IXwould have been established from the grounded battery, through thewinding T through the normally closed contacts 82' and 83 of thereleasing relay associated with the trunk IX, through the alternatecontacts 84 and 78 of the release relay associated with the busy trunkVIII, through the alternate contacts 116 and 79 of the energized releaserelay 69 of the busy trunk VII, through the contacts 80- and 81 of themagnet T of the trunk seized by the calling line, and back to ground. Itis thus apparent that the trunks are seized in rotation.

The foregoing operations occur upon the removal of receiver at thesub-station A, and before the impulses are sent in for the first digitof the desirednumber. hen the subscribers dial 8 is operated in theusual manner for the first digit two, it causes the subscribers line tobe momentarily opened twice, to break. the energizing circuitof the linerelay 66 of the selector E twice. The release relay 69 beingslow-acting, does not de-energize, as its circuit is momentarily brokenat the front contact of the relay 66; therefore the engagement of thearmature of the relay 66 with its back contact completes a circuit forthe primary stepping magnet PM of the selector E which extends fromgrounded battery, through the side switch wiper 85 and its firstposition con tact, through the winding of the primary magnet PM, throughthe winding of the slow-acting relay 86, through the alternate contacts87 and 88 of the slow-acting relay 69, through the back contact ofline-relay 66, and back to ground. The primary magnet PM energizes twiceover this circuit to lift the shaft and shaft wipers two steps oppositethe second level of bank contacts.

The relay 86 energizes on the first impulse,

but, being slow-acting, does not de-energize until the last impulse issent in. In its energized position the relay 86 completes a circuitthrough the private magnet ESQ over acircuit extending from groundedbattery through the'winding of the magnet E50, and through the frontcontact to relay 86 to ground. As soon as the slow-relay 86tie-energizes, the circuit of the private magnet is broken, which in'turn de-energizes and permits the side switch to pass to the secondposition. The passing of side switchwiper 85 to second position shiftsthe battery connection from the primary to thesecondary magnet SM. Thewiper 89 in second position, connects the private wiper 9O wit-h theprivate magnet ESC. As soonas thebattery is shifted to the circuit ofthe secondary magnet SM, a circuit is closed extending from groundedbattery, through the side switch wiper 85 and its second positioncontact through the winding of the slow-acting relay 91, through thewinding of the secondary magnet SM, through the armature and backcon-tact of the magnet SM to ground.

The secondary magnet energizes over this circuit to rotate the shaft andshaft wipers one step, breaks its own circuit at its armature andcontact,- and presses down the private magnet armature. The breaking ofits own circuit at its armature contact causes it to' de-energize. idle,the private magnet armature will return to normal position, therebypermitting the side switch to pass to third position. If, however, thefirst contact is busy, the first private bank contact will have aguarding ground upon it, as will be explained later. The private wiper,-90,.upon engaging, the grounded contact, completes a circuit extendingfrom the bank contact through the private wiper 90, side switch wiper89-(in second position) and winding of the private 'inagnet ESQ togrounded battery. Thus it is evident that the mains insecond position,and, consequently, the'secondary magnet continues to energize toro'tate'the'shaft and shaft wipers to an idle contact.

The passing of the side switch wipers 67 and 68 to third positionextends the calling line to the connector F. The extending of the lineto the connector closes the circuit of the line relay 92 of theconnector in the same manner as it did that of the relay 66 of the firstselector. The-energizing of the relay 92 closes a circuit through theslowacting relay 93, which energizes to provide a holding circuit forthe relay 69 over a circuit extending. from grounded battery through thewinding of the relay 69, through the back contact and 91, through thethird position contact and side switch wiper 89, over the private wiper90, and the corresponding bank contactof all the selectorsthathaveacc'ess tothe connector F, through the front contact and armature ofthe relay 93, and "through the side If the first contact is side switchre-' armature of the relay switch wiper 94k and its first positioncontact to ground. A short period of time elapses between the time thatthe side switch wiper 89 leaves the second-position and the time thattheguarding ground is supplied to the private bank contact by theconnector.. The relay 91 is put in for the'purposeof supplying aguarding ground to theprivate bank contacts during this time. It wilhberemembered that therelay 91 was energized in series with the secondarymagnet and, being a slow relay, it remains held up a short time aftertheside switch has passed to third position, thereby putting. a groundon the private wiper from ground at its front contact, through itsarmature in its alternate position through the side switch wiper 89 andits" third position contact to theprivate wiper 90. It is evident thatthe relay 69 must be slower than the relay91 to prevent the selectorfrom releasing. The apparatus is now ready for the second digit two. I

The subscriber A operates the dial for the second digit in the samemanner as for the the first digit. The relay 92 de-energizes twice toclose a circuit through the primary magnet PM extend-ing fromgroundedbattery through the winding, of the slow-acting relay '9 5,through theside switch wiper 96 and its first positionc ontact, through the windingof the primary magnet PM, through the front contact and left handarmature of the slow-acting. relay 93, and through the backcontactandarmature of thelinerelay 92 to ground. The primary. magnet PMenergizes over this c cuit to raise the shaft and shaft wipers 9i, 8 and99 two steps and opposite the second vel of bank contacts. As soon asthe snaft is lifted. the springs 100 and 101 engage preparing a circuitfor the release magnet REL.. The relay 95 alsoenergizes in the circuitwith the vertical magnet to cause its armatiires to break with theirback contacts and to make with their front contacts. Theleft handarmature closes a circuit which extends from grounded battery throughthe private magnet ESQ through the left hand armature andfront contactof slowirela'y 95-to ground. The relay 95 remains energizeduntil afterthe last impulse of the digit has been sent when it de=energizes therebybreaking the circuit of the private magnet.

Upon deenergization of the private magnet,

the side switch wipers escape to the second position. i i i The passingthe'side switch wipei'j'96 to the second'p'osition disconnects-theprimary magnet and placesv the secondary magnet SM in't-he ci'rcuit withtheslow relay 95. The switch is now in position to receive the impulsesfor the third or last digit five. As the dial is operated for this digitthe circuit of the relay 92'is broken five times, as before. The "relayde-energizes five times,

each time closing a circuit extending from grounded battery, through thewinding of slow relay 95, through the side switch wiper 96 and itssecond position contact, through the winding of the secondary magnet SM,through the outer left hand armature and back contact of relay 102,through the front contact and armature of slow relay 93, and through theback contact and armature of line relay 92 to ground. The secondarymagnet energizes five times to rotate the shaft and shaft wipers ontothe bank contacts of the called line #225. The relay 95 energizes on thefirst impulse as before, and de-energizes a moment after the lastimpulse has been sent in, thereby permitting the side switch to pass tothe third position. The passing of wipers 103 and 104 to third positionconnects the calling line to the called sub-station through thecondensers 105 and 106. The passing of the wiper 94 from the secondposition to the third position removes the ground connection, whichduring the first and second positions of the side switch has been placedon the circuit extending through the right hand armature and frontcontact of slow relay 93 to the private bank contacts of all selectorshaving access to the connector F, for guarding the switch F againstseizure and for holding the release relay 69 of selector E energized,and connects a new holding ground for this circuit, from the armatureand front contact of line relay 92. in its third position the wiper 107extends a ground connection to the relay 108, and coin pletes a circuitthrough the inner left hand armature and back contact of relay 102,through the private wiper 99 and back contact to the cutofi relay of thecalled line (similar to cut-off relay 74: of the calling line). The sideswitch wiper 96 of the connector in its third position, serves to closea circuit for the ringer relay 109. This circuit extends from groundedbattery through the slow relay 95, through the side switch wiper 96 andits third position contact, through the winding of the ringer relay 109,through the left-hand back contact of relay 108, through the ringinginterrupter 110 to ground. The ringer relay is energized intermittentlytodisconnect the calling line and connect the called line with theringing current generator L. A ringing current then flows from generatorL through the front contact and left hand armature of ringer relay 109,through the side switch wiper 10 through the switch wiper 98, throughthe bank contact and lower line conductor, through the bell 111 at thecalled subscribers station, through the upper line conductor, bankcontact, switch wiper 97, through the side switch wiper 103, through theright hand armature and front contact of relay 109, back to thegenerator L.

The subscriber at sub-station A removes the receiver in response to thesignal, and thereby closes an energizing circuit as soon as relay 109again de-energizes, should it be pulled up at the time, through the backbridge relay 108 of the connector. This circuit extends from groundedbattery through the left-hand winding of relay 108, through the backcontact and right hand armature of relay 109, through the side switchwiper 103 through the switch wiper 97, out over the subscribers line,back through the switch wiper 98, side switch wiper 104, left handarmature and back con tact of relay 109, through the right hand windingof back bridge relay 108 to ground at the side switch wiper 107 Thus thecalled subscriber is supplied with talking current. The relay 108energizes over the circuit just traced to break the circuit of theringer relay 109 at its left hand armature contacts.

After the conversation is completed, the release of the central officeapparatus used in the foregoing call is initiated by the callingsubscriber hanging up his receiver. The release is as follows: Thebreaking of the line at the sub-station, breaks the circuit of linerelay 92- at the connector F which in turn deenergizes thereby breakingthe holding ground for the release relay 69 of selector E and for therelease relay 93 of connector F. The release relay 69 upon deenergizingcloses a circuit for the release magnet REL which extends from groundedbattery through the winding of the mag net REL, through the contact 113and 114 closed when the switch E took its first step oif normal, throughthe contacts 115 and 88 of the release relay 69, and through the backcontact and armature of line relay 66 to ground. The release circuit forconnector F, extends from grounded battery through the winding of'release magnet REL, through contacts 101 and 100, through the backcontact and left hand armature of relay 93, and to ground through theback contact and armature of line relay 92. Upon the deenergization ofrelease relay 69, the locking circuit for connecting relay 8 of thecalling line and. the circuit through the calling line cut-off relay 7 1are opened.

The de-energization of the calling line cut-off relay, andde-energization of relay 8, restores all apparatus individual to thecalling line to normal. The energization of the selector release magnetREL permits the switch to return to normal thereby separating thesprings 113 and 114C. The energizetion of the connector release magnetREL in a similar manner permits the switch to return to normal therebyseparating the springs 100 and 101. Thus all apparatus is restored tonormal position and in readiness for another call.

-magnet ESQ to grounded battery. The

- have passed to the third positiombut Returning now to that point inthe operation of the connector while the'side switch is yet in thesecond position, had the called line been busy, the side switchwould-not would have been locked in the second position by the privatemagnet remaining energized.

The circuit through the private magnet 3 contact would have been fromthe bank upon which the wiper 99 is resting, WhlCh. contact would havebeen grounded, through v the wiper 99, back contact and inner left handarmature of relay 102, right hand winding of back bridge relay 108, backcontact and left hand armatureof ringer relay 109, side switch 104 andits second position contact, back contact and armature of relay 95, andthrough the Winding of private simultaneous energization of privatemagnet E80 and relay 108, closes acircuit through the busy relay 102.This circuit extends from ground through the right hand armature andback contact of relay 95, through the armature. and front contact ofprivate magnet ESC, through the busy relay 102 and through theright-hand armacontact of: relay 108 to ture and front grounded battery.The relay 102 energizes over this circuit to disconnect the'secondary Ymagnet SM at its back contact'and outer left hand armature and to shiftthe holding ground for relay 108 and private magnet. ESC to groundthrough its inner left hand armature and front contact. "Relay 102 alsocauses a busy signal to be sent to the calling subscriber over a circuitextending from grounded battery through the secondary of the inductioncoil 120 of the busy signalling machine M, through the right handarmature and front contact of relay 102, through the side switch wiper103 and its second position contact, through the right hand armature andbackcontact of ringer relay 109, through the condenser 105, thence overtheheavy conductors to and through the contact of the inner sub-stationA, back over the heavy conductors through the left-hand winding oftherelay 92 to ground.

The object inshifting the ground from the private wiper 99 to ground atthe front left hand armature of relay 102 is to prevent the side switchmagnet from de-energizing should the guarding potential be'removedbefore the switch F has been released. The release 1' of the switches incase the called line is busy is the same as if the connection had beenobtained. Many modifications of the invention other than thoseenumerated will readily suggest themselvesto those skilled inthe art,and' the'inventlon should thereforebe limited merely by the scope of theclaims.

I claim: I

1. I In a telephone "exchange system, :a subscribers line, agroup;voftrunk lines, multiple contact sets: for said subscribers line forconnecting said line to any one of said trunk lines, a connecting relayfor said subscribersline, armatures for said relay each individual to acontact set, means individual to each trunk line for predetermining anarmature for response to the energization of said relay, and means forpre-selecting an idle trunk line whereby said last named means isrendered effective. I

2. In a telephone exchange system, a-subscribers line, a group; of trunklines, mu-ltiple contact sets'for .said subscriber s'line for connectingsaid line to any one of said trunk lines, a connecting relay for saidsubscribersline, normally"inoperative armatures for said relay eachindividual to a contactset, means individual to each trunk line foroperatively positioning. an armature for response to the energization ofsaid relay, and means for pre-selecting an idle trunk line whereby saidlastnamed means is rendered effective.

'3. In a telephone exchange system,- a subscribersline, a group of trunklines, multiple contact sets for said subscribers line for connectingsaid line to any one of said trunk lines, a connecting relay; for saidsubscribers line, armatures for said relay normally positioned outsideof its stray magnetic field and each individual; toa contactset,1neansindividual to each trunk line I for positioning an armature fo to theenergization ofsaid relay, and means" forpre-selecting an idle trunkline whereby said last named means is renderedeffective. j

4. In a telephone exchange system, a subscribers line, a group of'trunklines, multiple contact-sets for connecting said line: to anyone of'saidtrunk lines, a connecting relay for saidsubscribers line, armatures forsaid relay each individual to a contact set, means tending normally toposition said armatures beyond the-magnetic influence of said relay,means individual to each trunk line for moving an armature to such aposition that-upon ener gization of said relay said armature is at-.trac-ted, andmeans. for'pre-selecting an idle trunk li'ne whereby saidlast named means is rendered effective;

In a telephone exchange system, a 0 group of subscribers"lines; agroupof trunk r response lines, a switching unit for connecting'iany forsaid subscribers line Y ual to each spouse to the energization of saidrelay, and means for pre-selecting an idle trunk line of the groupwhereby said last named means is rendered effective.

6. In a telephone exchange system, a group of subscribers lines, a groupof trunk lines, a switching unit for connecting any subscribers line ofthe group to any trunk line of the group of trunks, said switching unitcomprising a connecting relay individual to each subscribers line, eachsaid relay having ture corresponding to each trunk line for controllingthe connection of the line to said trunk lines, means individual to eachtrunk line for o Jerativel I oositionin the armature correspondingthereto for res onse to the energization of said relay, and means forpie-selecting an idle trunk line of the group whereby said last namedmeans is rendered efiective.

'7.- In a telephone exchange system, a group of subscribers lines, agroup of trunk lines, a switching unit for connecting any subscribersline of the group to any trunk line of the group'of trunks, said. sitching unit comprising a connecting relay individsubscribefls line,each said relay having an armature normally positioned outside of thestray magnetic field thereof corresponding to each trunk line forresponse to the energization of said relay,

line for po- I means individual to each trunk sitioning the armaturecorresponding thereto for response to the energization of said relay,and means for pro-selecting an idle trunk line of the group Whereb saidlast named means is rendered effective.

8. In a telephone exchange system, a group of subscribers lines, a groupof trunk lines, a switching unit for connecting any subscribers line ofthe group to any trunk line of the group of trunks, said switching unitcomprising a frame, connecting relays individual to said subscriberslines superim posed in said frame, each said relay having a normallyinoperative armature corresponding to each trunk line for controllingthe connection of the line to which it is individual to said trunklines, and means individual to each trunk line for operativelypositioning the armature corresponding thereto of each relay forresponse whereby upon the energization of one of said relays itsoperatively positioned armature will become attracted to extend thecalling line to the trunk. I

9. In a telephone exchange system, a group of subscribers lines, a groupof trunk lines, a switching unit for connecting any subscribers line ofthe group to any trunk line of the group of trunks, said switching unitcomprising a frame,-connecting relays individual to said subscriberslines superimposed in said frame, each said relay hava normallyinoperative armaing an armature normally positioned beyond the magneticinfluence of said relay and corresponding to each trunk line forcontrolling the connection of the line to which it is individual to saidtrunk lines, a trunk rod individual to each trunk line ournaled in saidframe and provided with means for moving the armature correspondingthereto of each relay into magnetic proximity to such relay, and amagnet for operating each of said rods.

10. In a telephone exchange system, a group of subscribers lines, agroup of trunk lines, a switching unit for connecting any subscribersline of the group to any trunk line of the group of trunks, saidswitching unit comprising a frame, connecting relays individual to saidsubscribers lines superimposed in said frame, each said relay having anarmature normally positioned beyond the magnetic influence of said rela7 and corresponding to each trunk line for controlling the connection ofthe line to which it is individual to said trunk lines, a trunk rodindividual to each trunk line journaled in said frame and provided withmeans for moving the armature corresponding thereto of each relay intomagnetic proximity to such relay, a magnet for operating each of saidrods, and means for energizing one of said magnets to pro-select a trunkline for use. v

11. In a telephone exchange system, a group of subscribers lines, agroup of trunk lines, a switching unit for connecting any subscribersline of the group to any trunk line of the group of trunks, saidswitching unit comprising a frame, connecting relays individual to saidsubscribers lines superimposed in said frame,.each said relay having anarmature normally positioned beyond the magnetic influence of said relayand corresponding to each trunk line for controlling the connection ofthe line to which it is individual to said trunk lines, a trunk rodindividual to each trunk line journaled in said frame and provided withmeans for moving the armature corresponding thereto of each relay intomagnetic proximity to such relay,a magnet for operating each of saidrods, means for energizing one of said magnets to pro-select a trunkline for use, and means for locking said operated rod in its rotatedposition. i

12. In a telephone-exchange system, a group of subscribers lines, agroup of trunk lines, a switching unit for connecting any subscribersline of the group to any trunk line of the group of trunks, saidswitching unit comprising a frame, connecting relays individual to saidsubscribers lines superimposed in said frame, each said relay having anarmature normally positioned beyond the ma netic. influence of saidrelay and corresponding to each trunk line for controlling theconnection of'the 'li-neto which it is individual to said trunk lines, atrunk rod individual to each trunk line journaled in said frame andprovided with means for moving the armature corresponding thereto ofeach relay into magnetic proximity to' such relay, a magnetfor operatingeach of said rods, means for energizing one of said magnets to'pre-select'a trunk linefor use, means for locking said operated-rod inits rotated position, and said rod upon connection of a subscribers lineto the pre-selected trunk.

13.1n a'telephone exchange system, a switching unit comprising ity ofsuperimposed relays supported lII'SiilCl frame, a plurality of armaturesfor each of said relays normally held beyond the magnetic influence ofsaid relay windings, verti- 'ally disposed rods journaled within theframe in alinement with corresponding armatures of each of said relays,cam pins on said rods for engagement with said armatures, and a magnetfor-each of said rods for rotating said rods to selectively position thearmatures of said relays for attraction.

14:. In a telephone exchange system, a switching unit comprising aframe, a plurality of superimposed relays supported in said frame, aplurality of armatures for each of said relays normally held beyond themagnetic influence of said relay windings, vertically disposed rodsjournaled within the frame in alin'eme-nt with corresponding armaturesof each of said relays, cam pins on said rods for engagement with saidarmatures, a magnet for each of said rods for rotating said rodstoselectively position the armatures of said relays for attraction, andmeans for locking each rod in its operated position.

15. In a telephone exchange system, a switching unit comprising a frame,a plurality of superimposed relays supported in said frame, a pluralityof armatures for'each of said relays normally magnetic influence of saidrelay windings,

vertically disposed rods journaled within the frame in alinement withcorresponding armatures of each of said relays, cam pins on said rodsfor engagement with said armatures, a magnet for each of said rods forrotating said rods to selectively position the armatures of said relaysfor attraction, means for looking each rod in its operated position, andmeans for unlocking each of said rods.

16. In a telephone exchange system, a subscribers line, a group of trunklines, multiple contact sets for said subscribers line for connectingsaid line to any one of said trunk lines, a connecting relay for saidsubscribers line, operating means individual to said relay for each ofsaid contact sets,

means for unlocking a frame, a pluralgroup of subscribers lines,

' tiple contact sets held beyond the "for each of said trunk meansindividual to eachtrunltline {for-predetermining one of saidfirs t namedmeans for operation, and means fo-rpreselectingan idle trunk linewhereby said'last named means is rendered effective,

17. In a telephone exchange system, a group of subscribers" lines, agroup oftrunk lines, switching mechanism comprising multiple contactsets for e'achsubscribers line for connecting such subscribers linetoany trunk line of the group of trunk lines,a connecting relay foreachysubscribefs line and operating means individual to said relay foreach of said contact sets, a relay individual to each of said trunklines, and means comprising said last named relays, operative uponconnection of a subscribers line to a trunk line for preselectingthe'next whereby said trunklines are selected for use in rotation. V p i18. In a telephone exchange system, a a groupof trunk lines, switchingmechanism comprisingmulfor each subscribers line for connecting suchsubscribers line to "any trunk line of the group of'trunk'linesaconnecting relay for each subscribers line and operating meansindividual to said relay for each of said contact sets, a relayindividual to each trunk line and operatiye upon the extension of asubscribers: line thereto, and means comprising the interconnected:contacts of said last named relays for preselecting an idle trunk linefor usewhereby said trunk lines are selected in'rotation.

19. In a telephone exchange system, a group of subscribers lines, agroupoftrunk lines, switching mechanism comprisingmuh. tiple contact sets foreach subscribers' line for connecting such subscriber s lineto any trunkline of the group of trunk lines, a connecting relay'for eachsubscribers line;,and

operating means individual toasaidrelay-for each of sa d contact sets,

a relay individual to each trunk line and operative'fupon the extensionof a subscribers line "thereto, means for interconnecting the contactsof said last named relays,

lines for predetermining one of said operating means for operation, andmeans comprising said relays and interconnecting means for operating aselecting magnet corresponding to the next succeeding idle trunk line ofthe group whereby said trunk lines are selected for use in rotation.

20. In a. telephone exchange system, a group of subscribers lines, agroup of trunk lines terminating in a group of firstselector switches, aswitching unit comprising multiple contact sets for each subscribersline for connecting such subscribers line to any trunk line of thegroupof trunk lines,

a selecting magnet nets operated, means controlled a connecting relayfor each subscribers line andoperating means individual to said relayfor each of said contact sets, a relay in each of said selector switchesadapted to be energized upon the extension of a subscribers linethereto, trunk preselecting magnets in said switching unit correspondingto and controlled by said last named relays respectively predeterminingone of said operating means for operation, and means comprising saidfirst named relays, operative upon oonnection of a subscribers line to apreselected trunk line for causing the energization of the trunkpreselecting magnet of the next succeeding idle trunk line of the groupwhereby said trunk lines are selected for use in rotation.

21. In a telephone system, a cross-bar switch comprising a plurality oflinemagnets, a plurality of trunk bar magnets, a relay associated witheach of said trunk bar magnets, means controlled by said relays forholding a single one of said trunk bar magnets operated, and meanscontrolled by said line magnets for energizing said relay associatedwith said operated trunk bar magnet.

22. In a telephone system, a cross-bar switch comprising a plurality ofline magnets, a plurality of trunk bar magnets, a relay associated witheach of said trunk bar magnets, means controlled by said relays forholding one of said trunk bar magnets operated, and means controlled bysaid energized line magnet and said operated trunk bar magnet forenergizing the relay associated with said trunk bar magnet.

23. In a telephone system, a crossbar switch comprising a plurality ofline magnets, a plurality of trunk bar magnets, a relay associated witheach of said trunk bar magnets, means controlled by said relays forholding a single one of said trunk bar magby said line magnets forenergizing said relay associated with said operated trunk bar magnet,and means controlled by said energized relay for releasing said operatedtrunk bar magnet and operating the next in order of said trunk barmagnets.

24. In a telephone system, a cross-bar switch comprising a plurality ofline magnets, a relay associated with each line magnet, a plurality oftrunk bar magnets, a relay associated with each of said trunk barmagnets, means controlled by said last relays for holding one of saidtrunk bar magnets operated, means controlled by said relays associatedwith said line magnets for energizing said associated line magnet, meanscontrolled by an energized line magnet for energizing said relayassociated with said operated trunk bar magnet, and means controlled bysaid last relays for releasing said associated trunk bar magnet andcausing the operation of the next in turn of said trunk bar magnets.

25. In a telephone system, incoming lines, outgoing lines, switchingmechanisms for connecting said incoming lines to said outgoing lines, amagnet for each of said incoming lines, an actuating bar for each ofsaid outgoing lines, said bars cooperating with said magnets to operatesaid switching mechanisms, a relay associated with each of said outgoinglines, and means under the control of each of said relays forpreoperating an actuating bar.

26. In a telephone system, incoming lines, outgoing lines, switchingmechanisms for connecting said incoming lines to said outgoing lines, amagnet for each of said incoming lines, an actuating bar for each ofsaid outgoing lines, said bars cooperating with said magnets to operatesaid switching mechanisms, a relay associated with each of said outgoinglines operated upon connection with said outgoing lines, and means underthe control of each of said relays for preoperating the next in order ofsaid actuating bars.

In testimony whereof I have ailixed my signature this twenty-seventh dayof September, 1919.

PERCY C. SMITH.

